The present invention relates to a laser beam scanning apparatus of the type used in apparatus such as a laser printer and a copier; and, more particularly, the invention relates to an electro-photographic apparatus having the capability of switching its resolution (print dot density).
An electro-photographic apparatus having a capability of having its resolution (print dot density) switched is disclosed in, for example, Japanese Patent Application Laid-Open No. 60-169820, Japanese Patent Application Laid-Open No. 6-11657, USP 5,006,705.
Japanese Patent Application Laid-Open No. 60-169820 discloses a technology where the beam pitch of a plurality of light beams and the diameter of the light beams are adjusted by adjusting a zoom lens provided in an optical system to form an image having a desired resolution.
Japanese Patent Application Laid-Open No. 6-11657 discloses a technology where an image forming position is adjusted or the pitch of light beams emitted from a plurality of light sources is varied by moving a lens in the direction of the optical axis.
U.S. Pat. No. 5,006,705 discloses a technology where the pitch between two light beams is varied depending on a desired dot density.
The above conventional technologies have the following disadvantages.
First of all, the constructions are complex since a zoom lens is required for adjusting the beam pitch and the light beam diameter in the case of Japanese Patent Application Laid-Open No. 60-169820, and a lens moving mechanism is required for moving the lens in the direction of the optical axis in the case of Japanese Patent Application Laid-Open No. 6-11657. Further, in the case of U.S. Pat. No. 5,006,705, there is a limitation to the changeable range of the dot density, because the light beam spot diameter is constant, and therefore the construction is not suitable for effecting a change in a wide range of print dot densities.